Precision matthews PM-1236 User manual

Brand: Precision matthews

Model: PM-1236

Category: Lathes

Type: User manual

PM-1236 v4 1-2017.indd

Model PM-1236 Lathe

High precision gap-bed machine

36 in. between centers, 12 in. swing over bed, 17-1/2 in. over gap

2 HP (1500W) motor, 220 Vac single phase

Speed range from 65 to 1810 rpm

Power cross-feed, traveling motor controls

D1-4 camlock spindle mount, 1-1/2 inch spindle bore

Weight, including stand, 1200 lb

PM-1236 with optional coolant system, live center and QC toolpost

701 Parkway View Drive

Pittsburgh, PA 15205

PM-1236 v4 1-2017.indd

PM-1236

FAQ

POWER light off, bottom arrow?

240 Vac power connected?

Circuit breaker in the electrical box

tripped?

E-STOP button in, top arrow?

Rotate it, should pop out.

My lathe doesn’t

run at all (1)

This manual contains essential safety advice on the proper setup, operation, maintenance, and service

of the PM-1236 lathe. Failure to read, understand and follow the manual may result in property damage

or serious personal injury.

There are many alternative ways to install and use a lathe. As the owner of the lathe you are solely re-

sponsible for its proper installation and safe use. Consider the material contained in this manual to be

advisory only. Precision Matthews, LLC cannot be held liable for injury or property damage during instal-

lation or use, or from negligence, improper training, machine modifications or misuse.

This manual describes PM-1236 machines as shipped from April 2016. There may be detail dif-

ferences between your specific machine and the information given here (with little or no impact on

functionality). If you have questions about any aspect of the manual or your machine, please call

412-787-2876 (east coast time), or email us at admin@machinetoolonline.com. Your feedback is

welcomed!

Belt cover in place? This closes the inter-

lock switch, bottom arrow.

FOOTBRAKE working, not stuck down?

If working properly, the footbrake should

close the microswitch, top arrow, opening

it when released.

CHUCK GUARD swung back? Close the

guard.

The motor didn’t run when

power was connected

My lathe doesn’t

run at all (2)

By design it should NOT run if the Motor

Control switch was UP or DOWN when

power is connected.

Electrical schematic, Section 5: Move

the Motor Control switch to neutral, mid

travel, to energise the power-switch-

ing contactor KA, thus restoring normal

conditions.

PM-1236 v4 1-2017.indd

Section 1 INSTALLATION

THESE ARE THE MAIN POINTS TO WATCH OUT FOR!

But read the following pages for more information

Handling the lathe is at least a two-man job.

Lifting gear – sling, hoist or forklift – must be rated for at least 1 ton.

Working location of the mill must allow space for removal of the belt cover at left, also ac-

cess to the coolant system (back of right hand cabinet) and the electrical box at the back

of the headstock.

Power requirement is 240V, 60Hz, 1φ, 20A circuit protection (spindle motor 14A full load).

Extension cord not recommended; if no alternative, use 12 AWG not longer than 20 ft.

Before connecting power be sure that:

The machine is on a firm footing, adequately secured to its stand.

Chuck camlocks tight, no wrench left in chuck.

Carriage and cross slide approx. mid-travel, power feed disengaged (Figure 1-10).

The headstock gear selectors are set for the lowest spindle speed.

•

1. Prepare the working location for the stand. If you in-

tend to use an engine hoist, there must be room for

the hoist, Figure 1-5. If not, a forklift and slings may

be a better option. If only an engine hoist is avail-

able, with limited space either side, the machine can

be fully assembled on a pair of 4-wheel dollies, then

rolled to its final position. The assembly can then be

raised by screw jack or other means to free the dol-

lies.

2. Position the LH and RH stand cabinets 34 inches

apart in the lathe’s final location. Mark the floor to

allow the cabinets to be repositioned in the same

locations for final assembly, when the front panel

and footbrake components have been installed.

3. Remove the coolant tank and pump assembly, if

supplied, from the RH cabinet, Figure 1-1.

4. Highly recommended!

Install leveling mounts rated for 250 lb each at the

corners of the two stand cabinets. (Alternatively,

plan on using metal shims under the cabinets to

level the lathe after securing it to the cabinets.)

5. Install front panel brackets on the two cabinets, Fig-

ure 1-2, using four M6 screws and washers.

SETTING UP THE LATHE

The PM-1236 is shipped in three packing cases, one for

the machine/chip tray/front panel/back splash, one each

for the left and right hand stand cabinets. The follow-

ing procedure makes use of an engine hoist, minimum

weight rating 1 ton.

Figure 1-1 Coolant pump and tank

Figure 1-2

In-facing side of cabinets

PM-1236 v4 1-2017.indd

Figure 1-4 Hoisting the lathe

Figure 1-3

Footbrake

components

6. With the RH cabinet in its approximate final location,

insert the footbrake pivot shaft, then locate the other

end of the shaft in the LH cabinet while easing the

cabinet into its final location.

7. Install the front panel on the brackets using four M6

screws, washers and nuts.

8. Position the chip tray on the stands, aligning the

6 holes for mounting bolts with the corresponding

threaded holes on top of the cabinets..

9. Unpack the footbrake components stowed in the

LH cabinet, then assemble the drawbar (2 pieces),

crank and extension spring as Figure 1-3 (see Foot-

brake adjustment, next page, also Stand and Cool-

ant Components diagram, Section 5).

10. Remove the packing case from the pallet, then un-

bolt the machine from the pallet.

11. Run two 1000 lb slings under the lathe bed and up

to the hoist hook. The slings must be inboard of the

leadscrew, feed shaft and motor control rod to

avoid damage to those components.

12. Slowly lift the lathe, controlling any tendency for it to

swing as it clears the pallet.

13. Roll the lathe into position, Figure 1-5, then hover it

an inch or so over the chip tray. This will allow you

to mark the perimeters of the lathe bed pedestals for

the purpose of caulking.

14. Apply a thick bead of silicone caulk just inside the

marked perimeters on the tray.

15. Lower the lathe onto the chip tray, making sure that

its six mounting holes are properly aligned. Excess

caulk squeezed out by the pedestals will form a

coolant-proof seal.

16. Install the six supplied M12 x 40 hex head bolts with

washers. Fully tighten the bolts. Re-check the caulk-

ing on both pedestals.

17. Install the backsplash using four M6 screws and

washers.

Figure 1-5 Lowering onto stand

CLEANUP

Metal surfaces may be protected by thick grease and/

or paper. Carefully remove these using a plastic paint

scraper, disposable rags and a light-oil such as WD-40.

PM-1236 v4 1-2017.indd

LEVELING

Make sure the lathe is in its permanent location. The

leveling procedure ensures that the lathe bed is in the

same state as it was when the lathe was checked for ac-

curacy in manufacture — level from end to end along the

bed, and from front to back. In other words, no warping.

Make sure all leveling mounts and/or shims are proper-

ly weight bearing, firmly in contact with the floor. Check

and adjust level from end to end using a “precision

machinist’s level”, if available. If not, use the most reli-

able level on hand. Check and adjust level front-to-back

across the bed using a matched pair of spacer blocks to

clear the Vee tenons on the bed ways. The blocks need

to be at least 1/4 inch thick, ground or otherwise accu-

rately dimensioned. Alternatively, check for level on the

ground surface of the cross slide as the carriage is tra-

versed from end to end. See also "Checking Alignment"

later in this section.

FOOTBRAKE ADJUSTMENT

This is a two-man procedure, see Figure 1-3:

Unhook the extension spring 1, and fully loosen all

four socket heads on the connecting sleeve 2.

While observing the switch arm and follower, Figure

1-6, raise the drawbar 3, adjusting the stop screw 4

to stop further upward movement of the drawbar at

the point where the microswitch is actuated, but no

further (additional travel may bend the switch arm).

Hook the extension spring onto its anchor bolt, then

raise the footbrake treadle to the desired height off

Figure 1-6 Footbrake switch

the floor.

Tighten all four socket heads on the connecting

sleeve.

While observing the footbrake switch as before, press

and release the treadle a few times to ensure that the

switch opens and closes reliably.

Lubricate the footbrake shaft.

CONNECTING POWER

As shipped. the PM-1236 is set for 220 V. If your supply

is nominally 240 V, it may be desirable to alter connec-

tions to the 24V transformer in the electrical box.

If the lathe did not come with a pre-installed power cord,

connect to the power source using 12 AWG (minimum)

3-wire cord through a strain relief bushing sized for the

electrical box ports. Depending on installed options and

other factors, the entry point shown in Figure 1-7 may

not be available. Connect the ground wire (PE) to the

grounding plate at bottom left. Connect L1, L2 to the left-

most two terminals on the bottom terminal strip.

Figure 1-7 Electrical box inputs/outputs

This configuration may vary depending on installed options, etc.

PM-1236 v4 1-2017.indd

INITIAL CHECKS

Read Section 3 if unsure about any item in the fol-

lowing

Check oil level (sight glasses) in the headstock,

the carriage feed gearbox, and the apron. See

Section 4, Figures 4-1 to 4-6.

Remove the belt cover left of the headstock. Make

sure the belt is properly tensioned and set for the

desired speed range. If not, re-position the belt,

Figure 1-8, also see Figure 3-4.

Figure 1-9 Forward/Reverse motor control

Mid-travel OFF, Down FORWARD, Up REVERSE

Figure 1-8 Drive belt adjustment

Set the spindle speed gear levers to B-1. Depend-

ing on the drive belt configuration, High or Low

speed, this will give a speed of 65 or 100 rpm. Do

not change speed when the motor is running.

Replace the belt cover.

If a chuck is installed check tightness of the three

Camlocks on the spindle nose, Figure 3-8.

Lower the chuck guard, if installed, Figure 1-9.

Check that there are no clamps or locks on moving

parts.

Check that the footbrake treadle is released (UP).

Set the carriage and cross slide to approximate

mid-travel.

Make certain that the power feed levers are disen-

gaged, Figure 1-10.

Make certain that the motor control switch is set to

OFF, mid-travel, Figure 1-9.

10.

11.

Figure 1-9 Chuck guard

Connect 220 Vac power. The power lamp (far left

of the orange color E-Stop button) should light,

unless circuit breaker QF1 in the electrical box has

tripped.

Be sure the E-Stop button has not been pushed in

(it should pop out when twisted clockwise).

Shift the motor control lever DOWN. The spindle

should turn forward, counter clockwise, viewed at

the chuck (nose) end.

Check the emergency function by pressing the E-

Stop button. The motor should stop. If this doesn’t

happen, the E-stop function is defective, and

needs attention.

Reset (twist) the E-Stop button to restore power.

Check that the chip guard switch stops the motor

when the guard is swung up.

Check that the belt cover interlock stops the motor

when the belt cover is removed.

Check that the footbrake stops the motor.

Return the motor control lever to OFF, mid-travel.

The motor should stop.

Shift the motor control lever UP. The spindle should

reverse, clockwise rotation, viewed at the chuck

(nose) end.

12.

13.

14.

15.

16.

17.

18.

19.

20.

21.

PM-1236 v4 1-2017.indd

OPTIONAL TEST RUN PROCEDURE

Run the spindle for a few minutes, forward and reverse,

at a selection of the 9 speeds available for the as-shipped

Vee belt configuration. See Section 3 if a different con-

figuration is preferred.

The carriage feed gearbox should also be run at this

time, but first make certain that the leadscrew and feed

shaft oilers at the tailstock end have been lubricated.

Also note: In initial tests, because the saddle and cross

slide should first be exercised manually, the leadscrew

split-nut should be disengaged — ditto the saddle/cross-

slide power feed lever, Figure 1-10.

After the initial test run, perhaps with a few additional

hours of machine time, some users drain and refill the

headstock and carriage feed gearbox. Lubricants are

specified in Section 4. Other users prefer to delay this

service action for at least 50 hours of running time. No

specific recommendation is given by the manufacturer.

Figure 1-10 Feed control levers on apron

ALIGNING THE LATHE

The most important attribute of a properly set up lathe

is its ability to “machine parallel”, to cut a cylinder of uni-

form diameter over its entire length. In other words, no

taper.

Leveling of the lathe is a part of this, see earlier in this

section. Equally important is the alignment of the center-

to-center axis with the lathe bed, as seen from above.

[Vertical alignment is nowhere near as critical, rarely

a cause of taper unless the lathe is damaged or badly

worn.] For more information see the final pages of Sec-

tion 4, Servicing the Lathe.

PM-1236 v4 1-2017.indd

Section 2 FEATURES & SPECIFICATIONS

MODEL PM-1236 Lathe

General information

The PM-1236 is a robust gap-bed lathe designed for day-in, day-out use in the model shop. Distance between

centers is 36 in., swing over the bed 12 in. With an all-up weight of 1000 lb, plus a wide range of speeds from 65

to 1810 rpm, the PM-1236 can handle far more than the typical small machine. The spindle nose is D1-4 Cam-

lock. A quick-change carriage feed gearbox provdes a full range of leadscrew ratios for U.S. and metric screw

cutting, together with an independent power feed for both saddle and cross slide. The power feed shaft is driven

through a friction clutch that allows the saddle to be stopped precisely at any point along the bed.

The spindle has a 1-1/2 in. clearance bore and MT5 internal taper. It runs in tapered-roller bearings, and is driven

by a 9-speed gearbox, coupled by Vee-belts to a 2 HP (1500 W) 220 Vac single-phase motor. Two-step pulleys

provide a choice of high and low speed drives, giving a total of 18 spindle speeds — 9 high range plus 9 low

range. A treadle-operated disc brake stops the spindle in milliseconds, even at the highest speeds. A circulating

coolant system (optional) may be installed in the right hand stand cabinet.

Supplied accessories

6 in. 3-jaw self centering chuck with two sets of jaws,

in-facing and out-facing

8 in. 4-jaw independent chuck with reversible jaws

Steady rest

Follower rest

Micrometer saddle stop

•

PM-1236 Floor plan: dimensions approximate (not to scale)

PM-1236 v4 1-2017.indd

PM-1236 SPECIFICATIONS

Including stand: Width 61-1/2 in., Height 55 in.

Depth 19 in. at chip tray, add 8 in. for cross slide

Weight (approximate numbers)

Lathe 960 lb net, 1020 lb shipping

Cabinet, left hand, incl. foot brake linkage

Cabinet, right hand, incl. coolant pump (option)

Power requirement 220 - 240Vac, 60 Hz, 1Ø, 12A full load

Motor TEFC type, cap start, 1.5 kW (2 HP), 1725 rpm

Work envelope

Distance between centers 36 in.

Gap insert length 9 in.

Swing over gap 17-1/2 in. diameter

Swing over bed 12 in. diameter

Swing over cross slide 7 in. diameter

Saddle travel 30-1/2 in.

Cross-slide travel 6-1/8 in.

Compound (top slide) travel 3-1/4 in.

Drive system

(High/Low belt drive with 9-speed gearbox)

Low range, rpm 65, 180, 200, 235, 330, 550, 700, 910, 1200

High range, rpm 100, 280, 300, 360, 500, 840, 1095, 1400, 1810

Carriage drive, thread cutting Leadscrew 8 tpi

Inch threads Choice of 36, from 4 to 60 tpi

Metric threads Choice of 32, from 0.4 to 7 mm pitch

Carriage drive, turning operations Choice of feed rates from 0.002 to 0.048 in./spindle rev

Cross slide drive Choice of feed rates from 0.001 to 0.009 in./spindle rev

Spindle

Chuck/faceplate attachment D1-4 Camlock

Internal taper MT5

Spindle bore Clearance for 1-1/2 in. diameter

Spindle length 15-5/8" overall

Tailstock

Internal taper MT3

Quill travel 4 in.

Work holding

Capacity, 1/8 in. to 6 in. diameter

Weight: 22 lb

Capacity: 3/8 in. to 8 in. diameter

Weight: 34 lb

Faceplate 10 in. diameter

Center rest (steady rest) capacity 3/16 to 1-1/2 in. diameter

Follower rest capacity 1/4 to 3/4 in. diameter

100 lb shipping weight, each

Dimensions, approximate overall

3-jaw chuck, 6 in., self-centering (scroll)

4-jaw chuck, 8 in., independent

PM-1236 v4 1-2017.indd

Everyday precautions

• This machine is intended for use by experienced users familiar with metal-

working hazards.

• Untrained or unsupervised operators risk serious injury.

• Wear ANSI-approved full-face or eye protection at all times when using the

machine (everyday eyeglasses are not reliable protection against flying par-

ticles).

• Wear proper apparel and non-slip footwear – be sure to prevent hair, clothing

or jewelry from becoming entangled in moving parts. Gloves – including tight-

fitting disposables – can be hazardous!

• Be sure the work area is properly lit.

• Never leave chuck keys, wrenches or other loose tools on the machine.

• Be sure the workpiece, toolholder(s) and machine ways are secure before

commencing operations.

• Use moderation: light cuts, low spindle speeds and slow table motion give

better, safer results than “hogging”.

• Don’t try to stop a moving spindle by hand – allow it to stop on its own.

• Disconnect 220 Vac power from the mill before maintenance operations such

as oiling or adjustments.

• Maintain the machine with care – check lubrication and adjustments daily

before use.

• Clean the machine routinely – remove chips by brush or vacuum, not com-

pressed air (which can force debris into the ways).

No list of precautions can cover everything.

You cannot be too careful!

PM-1236 v4 1-2017.indd

Section 3 USING THE LATHE

MOTOR CONTROLS

Before doing anything, check the installation in-

structions and power-up procedure in Section 1

Before connecting power to the lathe, be sure the motor

control lever is set to OFF, Figure 3-2. Connect the lathe

to a 220 Vac outlet — the POWER lamp should light

— then operate the motor control lever to run the spindle

in both directions.

Check that the following interlocks function correctly:

E-Stop button.

Chuck guard, if installed.

•

Figure 3-2 Set the motor control to OFF (mid travel)

SPINDLE DRIVE TRAIN

Two-step double-groove pulleys connect the motor to

the gearbox, Figure 3-3. The low speed configuration

gives spindle speeds from 65 to 1200, high speed from

100 to 1810 rpm. Because many users find that the low

range is suitable for most of their work, there is typically

no need to swap belts — unless a particular job calls for

a 50% speed increase. If the drive needs to be recon-

figured, Loosen the three hex head bolts securing the

Figure 3-3 Twin Vee belts drive the headstock gearbox

WHAT IS NOT IN THIS SECTION ...

The PM-1236 is a conventional engine lathe that re-

quires little explanation except for details specific to this

particular model — speed selection, thread cutting, and

the carriage/cross slide power feed system. Because

the user is assumed to be familiar with general purpose

metal lathes, this section contains very little tutorial.

CONTROL PANEL

In addition to three gear shift levers (speed and feed

direction) the main control panel also includes a “jog”

control. This a momentary type push-button indepen-

dent of the motor control switch right of the apron. When

operated, ithe jog button runs the spindle in the forward

direction, stopping when released.

Figure 3-1 Main control panel

Belt cover (to the left of the headstock).

Footbrake

•

PM-1236 v4 1-2017.indd

SPINDLE SPEEDS

The PM-1236 has a nine-speed headstock gearbox with

two shift levers C-B-A and 1-2-3, Figure 3-1. Before

changing speed, STOP THE MOTOR, Figure 3-2, then

move each shift lever to the desired setting. This may

need a little patience because it is not always possible to

go directly from one mesh to another. Move the spindle

back and forth by hand while trying to ease the lever into

its detent (meshed) position. Don’t use the JOG button

in this process — this may cause gear damage.

motor, Figure 3-4. Raise the motor to de-tension the Vee

belts. Move the belts to select the other speed range,

then lower the motor to re-tension. Make certain the mo-

tor is properly aligned, then re-tighten the bolts.

Figure 3-4 Motor bolts

SPINDLE SPEED (RPM)

1 2 3

HIGH

RANGE

A 360 1810 1095

B 100 500 300

C 280 1400 840

LOW

RANGE

A 235 1200 700

B 65 330 200

C 180 910 550

CHUCKS & FACEPLATE

The spindle nose on the PM-1236 accepts D1-4 Cam-

lock chucks, faceplates and other work holding devices.

A D1-4 chuck or faceplate is held by three threaded

studs, each with a D-shape crosscut to engage a corre-

sponding cam in the spindle nose, Figure 3-5. The func-

tion of the cams is to pull the chuck backplate inward to

locate its internal taper firmly on the spindle nose.

Alongside each stud is a stop screw, the head of which

fits closely in a groove at the threaded end of the stud.

The function of the stop screw is not to clamp the stud

in place, but instead to prevent it from being unscrewed

when the chuck is not installed.

Figure 3-5 Camlock stud

TO INSTALL A CHUCK

Disconnect the 220V supply from the lathe!

Chucks and faceplates are heavy — the 6 in. and 8 in.

chucks weigh 22 lb and 34 lb. They will cause serious

damage if allowed to fall. Even if a chuck is light enough

to be supported by one hand, the lathe bed should be

protected by a wood scrap, as Figure 3-6. Some users

add packing pieces, even custom-made cradles, to as-

sist “straight line” installation and removal.

Before installing make certain that the mating surfaces

of the chuck/faceplate and spindle are free of grit and

chips.

The cams on the spindle are turned with a square-tip

wrench similar to the chuck key (may be same tool in

some cases).

Recommended procedure:

Select the highest spindle speed (A-2) to allow easier

hand rotation of the spindle. (Alternatively, try moving

the speed selection levers between detents to find

CARRIAGE FEED DIRECTION

The lever below the speed selectors on the front panel,

Figure 3-1, determines whether the power feed is right

to left — the usual direction for turning and thread cutting

— or reversed. The selected direction applies to both the

leadscrew and the carriage/cross slide power feed.

Before changing feed direction, STOP THE MOTOR.

Hand-turn (jiggle) the spindle while feeling for the mesh,

as above

PM-1236 v4 1-2017.indd

Figure 3-7 Installing a Camlock chuck

Figure 3-6 Protect the lathe bed

a “between teeth” condition to disengage the gear

train.)

Turn the spindle by hand, checking that all three cam

markers are at 12 o’clock.

While supporting its full weight, install the chuck

without tilting, see Figure 3-7, then gently turn each

of the cams clockwise — snug, firm, but not locked

in this first pass.

Check that each of the cam markers lies between 3

and 6 o’clock, between the two Vees stamped on the

spindle, Figure 3-4.

If any cam marker is not within the Vees, first be sure

that there is no gap between chuck backplate and

spindle flange. Also, remove the chuck to inspect the

studs — burrs can be a problem, hone if necessary.

If there are no visible problems, the stud in ques-

tion may need adjustment as follows:

Remove the stop screw from the stud.

If the cam marker in question can’t get to the first

Vee (3 o’clock), back the stud OUT one full turn, then

•

replace the stop screw.

If the cam marker goes beyond the second Vee (6

o’clock), screw the stud IN one more turn, then re-

place the stop screw.

If the markers are correctly aligned, repeat the tight-

ening sequence as step 3, light force. Repeat the

sequence two more times, first with moderate force,

then fully tighten.

•

Figure 3-8 Cam in locked condition

TO REMOVE A CHUCK

Disconnect the 220V supply from the lathe!

Protect the lathe bed, as Figure 3-6. While supporting its

weight, turn each of the cams to 12 o’clock, Figure 3-7,

then remove the chuck. If the chuck does not come free,

try tapping the backplate gently with a soft (dead blow)

mallet.

CROSS SLIDE AND COMPOUND

The cross slide and compound, Figure 3-9, both have

10 TPI leadscrews, with 100-division graduated collars,

so each division represents a “real” motion of 0.001”. On

the cross slide dial, only, this shows as ϕ 0.002”, mean-

ing that a 0.001” depth of cut reduces the diameter of

the workpiece by 0.002”. The second row of divisions on

each collar reads in millimeters, 0.02 mm/division on the

compound, 0.04 mm/division on the cross slide. [These

collars have 127 divisions, so the reading is “true met-

ric”.]

PM-1236 v4 1-2017.indd

Figure 3-11 Carriage feed gearbox

CARRIAGE FEED GEARBOX

The rate of power feed relative to spindle speed is set

by the four shifter knobs below the main control panel,

Figure 3-11.

The S-M knob at right determines which is the driven

shaft, leadscrew (M) or carriage feed (S).

Unliike speed and feed direction changing at the main

control panel, there is no need to stop the motor while

selecting a different carriage feed. The same applies to

switching between M and S.

In the table on the following page, Figure 3-13, the ex-

ternal "change gears" are 24T and 48T, Figure 3-12 (24T

is the output from the headstock, 48T the input to the

carriage feed gearbox). This is a frequently used setup

for these two reasons:

Figure 3-9 Cross slide and compound dials

TAILSTOCK

The tailstock leadscrew is 10 TPI, with a travel of 4

inches. Like the compound, the tailstock has two gradu-

ated collars, one reading 0.001”/division, the other 0.02

mm/division. To remove tooling from the tailstock taper

(MT3) turn the handwheel counter-clockwise (handle

end view) until resistance is felt, then turn the handle a

little more to eject the tool. Conversely, to install a taper

tool make certain that the quill is out far enough to allow

firm seating.

For taper turning the tailstock may be offset by adjusting

the set screws on either side, arrowed in Figure 3-10.

To move the tailstock to the rear, for instance, the screw

on the lever side would be unscrewed, then the oppos-

ing set screw would be screwed in to move the upper

assembly.

Figure 3-10 Tailstock

A visual indication of the offset is provided by the scale,

but this is not a reliable measure for precise work. In

practice, the only way to determine the offset precisely

is to "cut and try' on the workpiece, homing in on the cor-

rect degree of offset in small increments.

The same issues arise when re-establishing "true zero"

of the tailstock, in other words returning it to the normal

axis for routine operations. One way to avoid cut-and-try

is to prepare in advance a bar of (say) 1" diameter qual-

ity ground stock, with precise center drillings at both

ends (do this by indicating for zero TIR in a 4-jaw chuck,

not in a 3-jaw unless known to be equally accurate). The

prepared bar can then be installed between centers and

indicated along its length.

PM-1236 v4 1-2017.indd

E2 E3 A2 E4 E1 C3 C4 A5 D5 B5

0.153 0.135 0.131 0.122 0.101 0.098 0.078 0.075 0.062 0.049

0.030 0.026 0.025 0.024 0.019 0.017 0.015 0.014 0.012 0.009

0.305 0.271 0.262 0.244 0.202 0.196 0.156 0.149 0.124 0.099

0.059 0.052 0.050 0.048 0.039 0.034 0.030 0.028 0.024 0.018

0.612 0.542 0.524 0.489 0.406 0.392 0.314 0.299 0.249 0.199

0.118 0.105 0.101

0.095 0.078 0.067 0.061 0.058 0.048 0.036

1.220 1.084 1.049 0.979 0.813 0.784 0.627 0.597 0.498 0.398

0.236 0.209 0.203 0.189 0.157 0.135 0.122 0.116 0.096 0.072

Movement per spindle revolution (mm)

E2 E3 A2 E4 E1 C3 C4 A5 D5 B5

0.0060 0.0053 0.0052 0.0048 0.0040 0.0039 0.0031 0.0030 0.0024 0.0019

0.0012 0.0010 0.0010

0.0009 0.0007 0.0007 0.0006 0.0006 0.0005 0.0004

0.0120 0.0107 0.0103 0.0096 0.0080 0.0077 0.0061 0.0059 0.0049 0.0039

0.0023 0.0020 0.0020 0.0019 0.0015 0.0013 0.0012 0.0011 0.0009 0.0007

0.0241 0.0213 0.0206 0.0193 0.0160 0.0154 0.0124 0.0118 0.0098 0.0078

0.0046 0.0041 0.0040 0.0037 0.0031 0.0026 0.0024 0.0023 0.0019 0.0014

0.0480 0.0427 0.0413 0.0385 0.0320 0.0309 0.0247 0.0235 0.0196 0.0157

0.0093 0.0082 0.0080 0.0074 0.0062 0.0053 0.0048 0.0046 0.0038 0.0028

Movement per spindle revolution (in.)

Carriage motion

Cross slide motion

S II

S I

METRIC

U.S.

1. It provides a useful range of carriage and cross feeds,

respectively (in./rev) carriage 0.0019 to 0.012, cross

slide 0.0004 to 0.0023.

2. It cuts 10 of the most popular U.S. threads found in

the model shop, simply by making gearbox selections.

In addition, the 24T/48T combination cuts the entire

range of metric pitches from 0.4 to 7 mm.

Note that switching from SI to SII doubles the feed rate.

Exchanging the gears (48T upper, 24T lower) increases

all speeds by a factor of 4.

Figure 3-12 External change gears

Figure 3-13

Table of feed rates

PM-1236 v4 1-2017.indd

ENGAGING THE POWER FEED

Power feed controls are located on the apron, Figure

3-14. The split-nut lever engages the leadscrew, and is

typically used only for thread cutting (S-M knob on gear

box set to M), described later.

The power feed lever is active only when the feed shaft

is rotating, S-M knob on gear box set to S. In its neutral

position the lever tip is captive between two offset stop

blocks. This prevents vertical movement of the lever un-

less it is first shifted to the left or right — a safety mea-

sure to avoid accidental engagement of the power feed.

Figure 3-14 Power feed levers on the apron

FEEDSHAFT CLUTCH

The clutch shown in Figure 3-15 disengages the power

feed if the carriage or cross slide hits an obstruction

when power feeding, thus minimizing the potential for

damage. This could be the result of either an accidental

event, or deliberately stopping the carriage at a precise

location set by the stop, Figure 3-16.

The clutch comprises a pair of spring loaded steel balls

bearing on a detent disc driven by the carriage feed

Figure 3-16 Micrometer carriage stop

Figure 3-15

Feedshaft clutch

gearbox. Spring pressure is adjusted by two set screws

on either side of the feed shaft, arrowed in Figure 3-15.

Setting the spring pressure is a process of aiming for the

best compromise between too high — damaging feed

pressure — and too low, which might mean unexpected

stopping for no good reason. Setting the clutch to work

reliably with the micrometer carriage stop is a good ex-

ample of such a compromise: start with low spring force,

then work up in small increments until the carriage stops

in the same location (say ± 0.002”, assuming a constant

depth of cut and feed rate).

CARRIAGE STOP

The stop asembly, Figure 3-16, has a micrometer-style

collar graduated in 0.001 in. divisions. It can be clamped

at any point along the lathe bed (two M6 socket head

screws on the underside secure the clamp plate to the

block). Make certain that the stop rod seats firmly on the

carriage casting, not on the rubber wiper.

Carriage feed — lever left & up

Cross slide feed — lever right & down

When engaging either power feed, move the lever gen-

tly, feeling for the gears to mesh as you go. If the gears

don’t engage at the first try, use the appropriate hand-

wheel to jiggle the carriage or cross slide, whichever one

you wish to move under power.

PM-1236 v4 1-2017.indd

COMPOUND SETUP FOR THREAD CUTTING

Thread cutting on the lathe is unlike most other turning

operations, for two reasons: 1. The cutting tool must be

precisely ground with an included angle of 60 degrees

for most American and metric threads, and; 2. It is pref-

erable to feed the tool into the workpiece at an angle so

it cuts mostly on the left flank of the thread. The correct

angle relative to the cross slide (zero degrees) is a sub-

ject of debate — should it be 29, 29-1/2 or 30 degrees?

Many machinists prefer 29 degrees because it holds

the cutting tool marginally clear of the right flank of the

thread, close enough for cleanup of the flank while at the

same time avoiding appreciable rubbing.

The 45

- 0

- 45

scale on the compound is not directly

helpful in setting the thread cutting angle, but it can be

used for that purpose if a second reference mark is ap-

plied to the cross slide. First make certain that the com-

pound is truly aligned with the lathe axis when 0

on the

scale is on the cross slide reference mark — do this by

indicating against a ground bar between centers while

advancing the indicator using only the compound. Allow

for the variance, if any, when applying the new reference

mark. Grind a chisel edge on a 1/4 in. square HS tool bit,

align it precisely on the left hand 30

scale mark; then,

wearing safety glasses, rap the tool bit sharply with a

hammer.

Figure 3-17 Setting up the compound for 30

infeed

A new reference mark is stamped on the cross slide at 30 de-

grees. To set the compound for thread cutting, rotate it clock-

wise to bring the right hand 30

scale mark in line with the new

reference mark. For 29

rotate the compound 1 degree more.

CHANGE GEARS FOR THREAD CUTTING

The large gears in Figure 3-12 are transposing gears,

120T and 127T. They allow a standard-thread leadscrew,

in this case 8 tpi, to cut metric threads. The transposing

gears are keyed together.

Key facts to remember:

For U.S. thread cutting, the 127T larger gear is simply

an idler, transferring the drive from the upper gear to the

lower gear. In this configuration, the spacer bushing is

outside the lower gear, as Figure 3-12.

For metric thread cutting, the lower gear is driven by the

120T transposing gear. In this configuration, not shown,

the spacer bushing is inside the lower gear.

Any change to the drive train typically calls for one or

both of the upper and lower gears to be exchanged for

For all TPI standard

threads (U.S.A.) the

127T gear is an idler

between upper and

lower gears.

by a larger or smaller gear. This will require the trans-

posing gear pair to be repositioned. The procedure for

this is:

Remove the M6 socket head screws from the upper •

Figure 3-18

Standard TPI setup

PM-1236 v4 1-2017.indd

STANDARD THREADS

Standard threads in the U.S.A., often referred to as “TPI”

(threads per inch), are mostly cut using the same exter-

nal gears as for the finer pitch metric threads — 24T up-

per, 48T lower. The table in Figure 3-19 lists all threads

available with that setup.

TPI TYPICAL USAGE (standard threads)

16 3/4 3/8

18 5/8 9/16 5/16

20 1/2 7/16 1/4

24 3/8 5/16 #12 #10

28 1/4 #12

32 #10 #8 #6

36 #8

40 1/4 #6 #5 #4

48 #4

56 #3

Figure 3-19 Popular threads cut with the 24T/48T setup

and lower gear shafts.

Remove the gears, washers, keys and bushing (lower

gear only).

While holding the gear support casting (quadrant)

with one hand, use a 15 mm wrench to loosen the

M10 hex nut hidden under the 127T gear. Allow the

casting to swing downward.

Loosen the M10 hex nut securing the transposing

gears to the support casting.

Install the upper and lower gears.

Bring the transposing gears into mesh with the lower

gear, trapping a scrap of bond paper (letter stock) be-

tween the two to hold them at the correct separation.

Tighten the transposing gears in position, then remove

the paper. Check for working clearance between the

gears.

Swing the gear support casting upward to mesh the

127T gear with the upper gear, again using a paper

scrap for separation.

Tighten the gear support casting.

•

CUTTING PROCEDURE FOR TPI THREADS

This procedure assumes that a single point thread cut-

ting tool will be used, and that the threading dial assem-

bly has been pivoted forward to engage worm gear with

leadscrew, Figure 3-14. Note that the threading dial is

not used for metric threads.

For metric and UNC/UNF threads the tool is ground to

a precise included angle of 60

. It is installed so that its

flanks are exactly 30

either side of the cross axis, ideal-

ly with the compound offset as Figure 3-17. Single-point

threads are cut in 10 or more successive passes, each

shaving a little more material off the workpiece.

To make the first thread-cutting pass the leadscrew is

run at the selected setting, Figure 3-20, and the carriage

is moved by hand to set the cutting tool at the starting

point of the thread. With the tool just grazing the work-

piece, the split-nut lever is lowered to engage the lead-

screw. This can be done at any point, provided the split-

nut remains engaged throughout the entire multi-pass

process.

When the first pass is completed, the tool is backed out

clear the workpiece (using the cross slide), and the spin-

dle is reversed to bring the carriage back to the starting

point. The cross slide is returned to its former setting,

then the tool is advanced a few thousandths by the com-

pound for the next pass. Each successive pass is done

in the same way, each with a slightly increased infeed

settting of the compound.

Many users save time by disengaging the split-nut at the

end of each pass, reversing the carriage by hand, then

re-engaging, usually by reference to the threading dial,

Figure 3-21.

If the TPI number is divisible by 4 re-engagement can be

done at any point — forget the threading dial.

For all other TPI numbers every engagement, includ-

ing the first, must at the point where a specific line

on the threading dial comes into alignment with the da-

tum mark. If not, the second and subsequent passes will

be out of sync. In some cases, Figure 3-21, there is a

choice of lines for re-engagement, but in every case the

process calls for careful timing. [NOTE: Disengagement

and re-engagement of the split-nut is not applicable to

metric threads].

Typical depths of cut per pass vary from an initial 0.005”

or so, to as little as 0.001”, even less. A finishing pass

or two with increments of only 0.0005” (or none at all)

to deal with the spring-back effect can make all the dif-

ference between a too-tight thread and one that runs

perfectly. Assuming that the compound is set over at

between 29 and 30 degrees, the total depth of cut is ap-

proximately 0.69 times the thread pitch, P (this equates

to a straight-in thread depth of 0.6 times P). There may

be a need for a few thousandths more in-feed than

0.69P, almost certainly not less.

PM-1236 v4 1-2017.indd

Figure 3-21 Using the threading dial

The dial worm gear has 16T; the leadscrew is 8 TPI,

so the carriage moves 2 inches for each revolution of

the dial when the split-nut is disengaged (when the

split-nut is engaged the dial is stationary).

The symbol "/" in the table means "forget the dial"

— engage at random for any TPI value that is an

even multiple of 4. For all other standard TPI threads

the split-nut is engaged when the datum coincides

with a specific line — or lines — on the threading dial.

1 - 8 Not the same as "/" (re-engage anywhere). Ap-

plies to TPI values that are odd multiples of 4; start on

any line (not a half space), re-engage on any line.

2.4.6.8 Applies to even number TPI values that are not multiples of 4 (10, 14, etc.): re-engage at the line you started with OR

any other line at right angles to it — start on 1, re-engage on 3, 5 or 7; or, start on 2, re-engage on 4, 6 or 8.

4.8 Applies to odd number TPI values (7, etc.): re-engage at the line you started with OR the diametrically opposite line — can

be any line pair, 1 & 5, 2 & 6, etc., not necessarily 4 & 8.

8 Applies to fractional values (4-1/2, etc.): re-engage on the same line you started with for the first pass — can be any line

number, not just the 8.

TPI Line TPI Line TPI Line TPI Line

4 / 8 / 16 / 32 /

4-1/2 8 9 4.8 18 2.4.6.8 36 1 - 8

9-1/2 8 19 8 38 2.4.6.8

5 4.8 10 2.4.6.8 20 1 - 8 40 /

5-1/2 8 11 4.8 22 2.4.6.8 44 1 - 8

6 4.8 12 1 - 8 24 / 48 /

6-1/2 8 13 4.8 26 2.4.6.8 52 1 - 8

7 4.8 14 2.4.6.8 28 1 - 8 56 /

7-1/2 8 15 4.8 30 2.4.6.8

THREADS PER INCH

UPPER

GEAR 24T

Speed

MII

16 18 19 20 22 24 26 28 30

32 36 38 40 44 48 52 56 60

Gearbox A2 A3 C3 A4 C3 C3 C3 A5 B4

Lower gear 48T, exceptions in RED 38 44 52

THREADS PER INCH

UPPER

GEAR 48T

Speed

MII

4 4-1/2 9-1/2 5 5-1/2 6 6-1/2 7 7-1/2

8 9 19 10 11 12 13 14 15

Gearbox A2 A3 C3 A4 C3 C3 C3 A5 B4

Lower gear 24T, exceptions in RED 38 22 26

Figure 3-20 Gear-

box and external

gear selections

for standard

threads

Figure 3-22

Threading dial

visualization for

selected U.S.

threads

PM-1236 v4 1-2017.indd

THREAD CUTTING (METRIC THREADS)

Practically all metric thread pitches from 0.4 mm to 1.75

mm are cut with one external gear setup: 24T upper,

48T lower. For thread pitches from 1.6 mm to 7 mm, the

inverse setup is used: 48T upper, 24T lower.

For metric thread cutting the split-nut on the apron must

be left engaged throughout the entire process. This

not the case for U.S. standard TPI threads, for which the

normal procedure is to disengage the half-nut after each

pass, reverse the carriage, then re-engage at a specific

indication on the threading dial (see above).

GEARS:

UPPER 24T

LOWER 48T

METRIC THREAD PITCHES (mm)

Speed

0.4 0.45 0.5 0.6 0.7 0.75

MII

0.8 0.9 1 1.2 1.25 1.4 1.5 1.75

Gearbox B4 C4 C3 C2 A4 D2 E4 A2 E2

GEARS:

UPPER 48T

LOWER 24T

METRIC THREAD PITCHES (mm)

Speed

1.6 1.8 2 2.25 2.4 2.5 2.8 3 3.5

MII

3.2 3.6 4 4.5 4.8 5 5.6 6 7

Gearbox B4 C4 C3 C2 A4 D2 E4 A2 E2

Figure 3-24 Table of metric pitches vs. gearbox settings

For all metric threads

the top gear drives

the 127T gear. The

lower gear is driven

by the 120T gear.

Figure 3-23

Metric setup

GAP BED

A 9 inch long section of the bed at the headstock end

can be removed to allow turning of diameters up to 17-

1/2 in., Figure 3-25.

Figure 3-25 Gap insert

To remove the gap insert back out the arrowed "pusher"

screw two or three turns, then remove the four large

socket head screws securing the insert to the bed. To

minimize cosmetic damage, cut through the paint and

filler along the joint between insert and bed using a

sharp knife or pointed scraper.

Using a 14 mm wrench jack out the two locating pins,

arrowed in Figure 3-26, then tap the insert free with a

Figure 3-26 Gap insert hardware

soft-face mallet.

Before re-installing the insert, be certain that all mating

surfaces are scrupulously clean. Set the insert in place,

lightly tap in the two locating pins, then install the four

large bolts (snug, but not fully tightened). Jack the insert

to the right with the pusher screw to close the gap, if any,

between the ground surfaces of the bed ways at the join

(a visible parting line is acceptable, but a discontinuity

that snags the carriage is not). If a satisfactory join can-

not be achieved, it may be necessary to remove and

reinstall the insert from scratch.

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Precision matthews PM-1236 User manual

Brand: Precision matthews

Model: PM-1236

Category: Lathes

Type: User manual

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Precision matthews PM-1236 User manual

Precision matthews PM-1236 User manual

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